Google Talk default installation does not allow users to set their online status. Your friends will always know when you are idle or active. There is a tool called galwaysidle to solve this problem. After you have installed it, you will be able to set your online status such as Always Active, Always Idle or the normal way.
After the installation, right click your google talk icon at the taskbar and you will see something like this:
Google Talk, Labs Edition is another version of google talk with additional features such as group chat, google calendar and Orkut notifications. If you use web googletalk before, you notice it can transform or rotate your smillies to a nice looking one. Previously this feature is not supported in the normal googletalk client, now the labs edition will have this feature included. However, in the Labs Edition, voice chat and file transfer is not included grrrrr.
If you are google calendar users and rely heavily on it for notifications, google talk labs edition is for you. You can customize how it notifies you and even snoop it. Yes, just like how you snoop your morning alarm clock.